1. Field of the Invention
This invention relates to a camera including a digital processing circuit of simple arrangement.
2. Description of the Related Art
In an attempt to replace the conventional optical silver-halide type camera, a camera called an electronic still camera has been developed. The electronic still camera is arranged to convert the image of a photographing object into an electrical image signal by means of an image sensor; to record the image signal on a recording medium; and to include a reproduction circuit for reproducing the signal recorded. FIG. 6 of the accompanying drawings shows an example of the camera of this kind.
According to the conventional arrangement of the electronic camera, the object image is allowed only for a moment to be formed on the image sensor 102 through a lens 100 and a shutter 101 and to be converted into electric charge. The electric charge is read out by means of an image sensor driving circuit 102-1 in synchronism with a synchronizing (hereinafter referred to as sync) signal which is generated by a sync signal generator (hereinafter referred to as SSG) 122. A motor 112 is controlled and rotated by a servo circuit 113 in synchronism with a sync signal generated also by the SSG 122. Upon completion of building-up of the rotation control (stabilization of speed), the servo circuit 113 sends a build-up detection signal to a system controller 123 to inform the latter of the stabilization of rotation of the motor 112. Upon receipt of this detection signal, the system controller 123 gives an instruction to the SSG 122 for commencement of reading from the image sensor 102. This causes the image sensor driving circuit 102-1 to read image data from the image sensor 102.
The image data read out from the image sensor 102 includes analog signals obtained from picture elements for the colors R (red), G (green) and B (blue). The R, G and B signals are amplified by an amplifier 103. The amplified signals are supplied via gamma correction circuits 140 to the white balance circuit 141. Meanwhile, external light which is obtained by a white balance sensor 142 is taken into an analog-to-digital (A/D) converter disposed within the system controller 123 and is then output through a digital-to-analog (D/A) converter which is also disposed within the system controller 123. The output of the D/A converter of the system controller 123 is supplied to the white balance circuit 141 to be used for adjusting the balance among the R, G and B signals. After that, the R, G and B signals are supplied to a matrix circuit 104 to be converted into a luminance signal Y and color-difference signals R-Y and B-Y. The color-difference signals R-Y and B-Y are converted into a line-sequential signal conforming to a still video format by outputting them in blocks of horizontal lines alternately through a switch 130 in accordance with a switching signal output from the SSG 122. The line-sequential color-difference signals thus output from the switch 130 are alternately supplied to a low-pass filter (LPF) 106. Meanwhile, the luminance signal Y is supplied to an adder 105-1 to be added together with a (horizontal/vertical) sync signal. After the adder 105-1, the luminance signal Y is supplied to an LPF 105 to remove all the signal components thereof that are outside a modulation band. The signal Y thus processed is supplied to a frequency modulator 107. The line-sequential color-difference signals output from the LPF 106 are frequency-modulated by another frequency modulator 108. The modulated wave of the luminance signal and those of the color-difference signals are frequency-multiplexed by an adder 107-1. The output of the adder 107-1 is supplied to an amplifier 109 to be amplified to a level apposite to recording.
The signal which is thus obtained from the amplifier 109 is supplied via a switch 135 to a recording head 130. The head 130 records the signal on a recording medium 131 in the form of, for example, concentric circles. A carriage 110 is arranged to shift the recording head 130 radially inward or outward over the circular surface of the recording medium 131. A PG sensor 111 is arranged to detect, every time the medium 131 makes one turn, a magnet provided on a center hub of the medium 131. A switch box 124 includes various operation switches.
In reproducing recorded signals from the medium, the head 130 is shifted by the head carriage 110 to a recorded track. A video signal recorded in the track is converted into an electrical signal. During the reproducing operation, the switch 135 acts to supply the electrical signal to a reproduction amplifier 115. The output of the amplifier 115 is then supplied to a band-pass filter (BPF) 116 and a low-pass filter (LPF) 117 respectively. The output of the BPF 116 and that of the LPF 117 are supplied to frequency demodulators 118 and 119 to be converted into the baseband signals of a luminance signal and color-difference signals respectively. The sync signal which is included in the luminance signal Y is separated into a horizontal sync signal H and a vertical sync signal V by a sync signal separation circuit 120. These sync signals are supplied via the SSG 122 to the servo circuit 113, etc., during the process of reproduction. The servo circuit 113 compares the phase of a reference signal output from the SSG 122 with that of an FG signal obtained from a motor 112 to obtain an error signal as the result of comparison. The servo circuit 113 then uses this error signal in rotating the motor 112 according to the signal reproduced.
The color-difference signals are in the line-sequential state as mentioned in the foregoing. During reproduction, therefore, they are converted into a line-simultaneous state through a line-simultaneous conversion circuit, which is formed jointly by a 1-H delay circuit HD, a switch 136 and a line sensing circuit 137. After this, the color-difference signals and the luminance signal are supplied to an NTSC encoder EN to be converted into an NTSC signal, which is supplied via an output terminal 126 to a monitor MO to be displayed in the form of a picture thereon.
The conventional electronic still camera which is arranged as described above, however, necessitates the use of a gain control circuit solely for the purpose of adjusting the white balance of the signals read out from the image sensor. In addition, it has been necessary to use memory means for compensating for a drop-out occurring in the reproduced signal, for correcting jitters, for the line-simultaneous conversion process, etc.